1. Field of the Invention
The present invention relates to a positive-type photosensitive resin composition, a cured layer, a protecting layer, and an insulating layer, and a semiconductor device and a display device using the layers.
2. Description of Related Art
A polyimide resin possessing excellent heat resistance and superior electrical and mechanical properties has been used for a surface protecting layer and interlayer dielectric of semiconductor chips. These days, a polybenzoxazole resin having excellent wet resistance reliability due to absence of a carbonyl group originating from a high polar imide ring is used in the latest semiconductor chips. A photosensitive resin composition comprising a polybenzoxazole resin or a polyimide resin which is provided with photosensitivity to simplify a part of a patterning process has been developed. The resin composition has an effect of shortening the process and increasing the yield.
More recently, a positive-type photosensitive resin composition which can be developed using an alkaline aqueous solution has been developed from the viewpoint of safety. For example, Patent Document 1 discloses a positive-type photosensitive resin composition which comprises a polybenzoxazole precursor as a base resin and a diazoquinone compound as a sensitizer. The composition has high heat resistance, outstanding electrical properties, and microfabricability and has a possibility of being used not only as a wafer coating material, but also as a resin composition for interlayer insulation. The development mechanism of the positive-type photosensitive resin composition is as follows. The diazoquinone compound in the unexposed area is insoluble in an alkaline aqueous solution. The base resin is provided with resistance to the alkaline aqueous solution as a result of an interaction with the diazoquinone compound. On the other hand, if exposed to light, the diazoquinone compound changes chemically and becomes soluble in an alkaline aqueous solution, and promotes dissolution of the base resin. A coated layer pattern consisting only of the resin in the unexposed area can be prepared by removing the exposed area by dissolution using the solubility difference of the exposed area and unexposed area patterning.
The polybenzoxazole precursor resin in the positive-type photosensitive resin composition from which the coating-layer pattern has been formed is dehydrated by ring-closing by curing at a temperature of about 300° C., whereby the precursor resin ultimately turns into a polybenzoxazole resin having high heat resistance. Remarkable miniaturization and high integration of semiconductor chips in recent years has reduced heat resistance, particularly of storage chips. In order to increase the yield, a polybenzoxazole precursor resin which can be cured at a lower temperature is demanded. The cyclization rate of the resin after curing is an important factor when curing the resin at a low temperature. A low cyclization rate causes a problem in reliability of the semiconductor device due to alkali-soluble groups remaining in the resin. Patent Document 2, for example, discloses a positive-type photosensitive resin composition comprising an alkali-soluble polyamide which has a polybenzoxazole precursor structure and a thermal latent acid generator. Wiring of the semiconductor chip is corroded by an acid generated with heat. Thus, the resin composition has the same problem of poor reliability.
Therefore, development of a positive-type photosensitive resin composition which satisfies reliability when cured at a low temperature is strongly desired.
[Patent Document 1] Japanese Patent Publication No. 1-46862
[Patent Document 2] WO2005/109099